1. Field of the Invention
The present invention relates to a discharge lamp lighting apparatus in which a discharge lamp is lighted according to electric characteristics appropriate to a type of the discharge lamp.
2. Description of Related Art
There are many types of high intensity discharge (HID) bulbs such as a D1 bulb, a D2 bulb, a D3 bulb and a D4 bulb representing a plurality of types of discharge lamps. In both the D1 bulb and the D2 bulb, mercury is packed in a discharge tube. Because mercury exists as liquid mercury at ordinary temperatures, mercury is rapidly evaporated in the discharge tube, almost white light radiates from the discharge tube, and a voltage between electrodes of the discharge tube is stably maintained to a comparatively high temperature during the lighting of the discharge tube.
However, because the use of mercury causes environmental problems, the use of mercury is suppressed, and both the D3 bulb and the D4 bulb not using mercury have been developed. In both the D3 bulb and the D4 bulb, metal different from mercury is substituted for mercury, and the substitutive metal exists as solid metal at ordinary temperatures. However, a discharge voltage in an discharge tube having the substitutive metal is lowered, and a high electric power is required to evaporate the substitutive metal in the discharge tube. In this case, a high electric power is required to rapidly light the D3 bulb or the D4 bulb.
Therefore, electric characteristics of both the D1 bulb and the D2 bulb in the lighting differ from those of both the D3 bulb and the D4 bulb. In cases where a conventional discharge lamp lighting apparatus is used to light various types of bulbs at the same luminous characteristics regardless of the difference in the electric characteristics between the D1/D2 bulb and the D3/D4 bulb, it is required that both an electric power supplied to the D1/D2 bulb and another electric power supplied to the D3/D4 bulb are prepared in the conventional discharge lamp lighting apparatus and one of the electric powers is selected in the conventional discharge lamp lighting apparatus in compliance with the type of the bulb connected to the conventional discharge lamp lighting apparatus. Therefore, a problem has arisen that it is troublesome to manually select one of the electric powers in the conventional discharge lamp lighting apparatus.
Also, a discharge lamp lighting device is disclosed in the Published Unexamined Japanese Patent Application No. 2001-210490. In this device, to light each of a plural kinds of discharge lamps with characteristics appropriate to the type of discharge lamp, a type of the discharge lamp connected to the device is specified according to a change of voltage or a change of current during a selecting time period at an initial stage of power supply or according to values obtained after the selecting time period, and an electric power appropriate to the specified type of the discharge lamp is supplied to the discharge lamp. However, a problem has arisen that an electric power appropriate to the type of the discharge lamp connected to the device cannot be supplied to the discharge lamp at the start of the lighting of the discharge lamp. Therefore, a life time of the discharge lamp is shortened, or the discharge lamp cannot be rapidly lighted at high luminance.
Also, another discharge lamp lighting device is disclosed in the Published Unexamined Japanese Patent Application No. H4-342988 (1992). In general, a discharge lamp is used so as to be lighted just after the putting out of the discharge lamp. Because the discharge lamp put out is maintained to a high temperature for a time, this lighting is called a hot start. Also, another discharge lamp is used so as to be lighted when the discharge lamp is set to a low temperature. This lighting is called a cold start. In this case, even though two discharge lamps are formed of the same type, characteristics of one discharge lamp operated at the hot start slightly differ from that operated at the cold start. Also, even though a plurality of discharge lamps of the same type are manufactured, characteristics of each discharge lamp slightly differ from those of the other discharge lamps due to the difference in manufacturing conditions or secular change. Therefore, when each of the discharge lamps formed of the same type is lighted by using a general discharge lamp lighting device, the light flux of one discharge lamp is slightly overshot or undershot, the life time of the discharge lamp is shortened, or the discharge lamp cannot be rapidly lighted at high luminance. To prevent this problem, in the discharge lamp lighting device of the Application No. H4-342988, characteristics of a discharge lamp lighted in a previous run are stored, and an electric power supplied to the discharge lamp in a current run is determined in the discharge lamp lighting device according to the stored electric characteristics to control the lighting of the discharge lamp. Therefore, one type of discharge lamps set to the same rated condition can be appropriately operated. However, in a case where one type of discharge lamp set to a rated condition is replaced with another type of discharge lamp which is set to a considerably different rated condition and required a considerably different electric power, a problem has arisen that an electric power appropriate to a type of a discharge lamp connected to the device cannot be always supplied to the discharge lamp.
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional discharge lamp lighting apparatus, a discharge lamp lighting apparatus in which any type of discharge lamp is efficiently lighted from the start of the lighting even though the type of discharge lamp is connected at present to the apparatus in place of another type of discharge lamp having electric characteristics different from those of the discharge lamp connected to the apparatus at present.
The object is achieved by the provision of a discharge lamp lighting apparatus including discharge lamp lighting means, electric characteristic detecting means, storing means and control means. An electric power is supplied to a discharge lamp by the discharge lamp lighting means. An electric characteristic of the electric power supplied to the discharge lamp in a preceding lighting operation is detected by the electric characteristic detecting means and is stored in the storing means. The control means judges a type of the discharge lamp according to the detected electric characteristic of the preceding lighting operation and controls the discharge lamp lighting means to produce a typical electric power of a typical electric characteristic appropriate to the judged type of the discharge lamp and to light the discharge lamp according to the typical electric power of the typical electric characteristic.
Therefore, even though a first discharge lamp is changed to a second discharge lamp of which a type and an electric characteristic differ from those of the first discharge lamp, the type of the second discharge lamp is judged according to the electric characteristic of the second discharge lamp in a preceding lighting operation, and the second discharge lamp is lighted from a lighting start time of a present lighting operation by receiving a typical electric power of a typical electric characteristic appropriate to the type of the second discharge lamp. Accordingly, the discharge lamp can be efficiently lighted from the start of the lighting even though the discharge lamp is connected at present to the discharge lamp lighting apparatus in place of another discharge lamp having different electric characteristics.
In another aspect of the present invention, a discharge lamp lighting apparatus includes a shape detecting means for detecting a shape of the discharge lamp discharge lamp lighting means. Therefore, a type of the discharge lamp can be judged according to a shape of the discharge lamp detected by the shape detecting means.